Re: Large writable variables

On 16/10/2018 08:30, Andres Freund wrote:
> This just reminded me that a couple times I wanted a cast that casts
> away const, but otherwise makes sure the type stays the same. I don't
> think there's a way to do that in C, but we can write one that verifies
> the cast doesn't do something bad if gcc is used:
>
> #if defined(HAVE__BUILTIN_TYPES_COMPATIBLE_P)
> #define unconstify(cst, var) StaticAssertExpr(__builtin_types_compatible_p(__typeof(var), const cst), "wrong cast"), (cst) (var)
> #else
> #define unconstify(cst, var) ((cst) (var))
> #endif
>
> Does anybody besides me see value in adding a cleaned up version of
> that?

I've had the attached patch lying around. As you can see there, there
are a few places where it could be useful, but not too many.

The name CONST_CAST() is adapted from C++.

Your version with __builtin_types_compatible_p() doesn't work for
casting between char * and const char *, so it wouldn't be very useful.

--
Peter Eisentraut http://www.2ndQuadrant.com/
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